Two more men aged 24 and 27 from the Cambridgeshire area have been arrested in connection with the murder of Sonny Grey.
They have since been released on police bail pending further enquiries.
Three other suspects arrested in December, two men from Cambridgeshire, aged 29 and 18, and a 29-year-old man from Lincolnshire, have been re-bailed.
A fourth man arrested in the murder inquiry in December has since died, reportedly believed to have killed himself.
The police are repeating their appeals for information on the murder of 70-year-old Romany traveller Sonny Grey on October 29, 2011.
He died in hospital from burns sustained by being scalded with a kettle by three robbers who attacked him at his home in Westwick Gardens, Lincoln.
Officers are also trying to recover jewellery stolen by the attackers from the scene.
Call Lincolnshire Police with information on 101, or call independent charity Crimestoppers anonymously on 0800 555 111.